Conventionally, there is known a method for detecting an object (visible object) visible from a designated point among objects existing in three dimensional space of a geographical information system. The method includes 3 stages: (1) detecting an object existing in sight, (2) determining, through rendering, geometric determination, or the like, whether or not the detected object is an invisible object such as an object which is located in the far distance and thus substantially invisible, and an object located at a blind spot of another object and (3) deleting the object determined as invisible. However, this detection lacks high speed performance.